The invention relates to a steering wheel with airbag module.
There is a problem with motor vehicle steering wheels owing to the rigid coupling with the steering column. Namely, that vibrations occur on the steering wheel at least in certain speed ranges. These vibrations are caused by the inherent frequency of the airbag/steering wheel depending on a certain engine speed. In order to reduce the vibrations, it is known to displace the inherent frequency of the airbag/steering wheel by applying an additional mass on the steering wheel in a frequency range which lies outside of the area of the vibrations actually occurring on the steering wheel. It is also known, for example, from DE 37 10 173 A1 to mount the housing of the airbag unit floating on the steering wheel but damped so that the airbag unit can move relative to the steering wheel across the longitudinal axis of the steering column.
It is additionally proposed that the housing can also move in the direction of the longitudinal axis of the steering column. The mobility is achieved by fixing retaining yokes on the sides of the housing wherein these yokes have in corresponding bores bearing bushes which have noise-damping properties. Retaining screws are guided through the bearing bushes for fixing the retaining yokes on the spokes of the steering wheel. A clearance is thereby provided between the shaft of each retaining screw and the relevant bush to allow lateral displacement of the retaining yokes relative to the retaining screws. Thus, a floating bearing is achieved. The entire airbag module, including the cap which screens the airbag from the passenger cell, is thereby mounted with a floating action.
The drawback with this arrangement is that when vibrations appear on the steering wheel, these vibrations are visible, inter alia, through the relative movement of the cap relative to the steering wheel. As the steering wheel vibrates as a result of the rigid coupling with the steering spindle, no or markedly reduced vibrations appear on the cap. Therefore, a relatively large gap has to be provided between the cap and the steering wheel in order to avoid the mutual friction and thus troublesome noises which occur when vibrations arise.
One object of the invention is therefore, in the case of a steering wheel, to eliminate at least substantially, a relative movement between the steering wheel and a cap which is mounted separately opposite the upper side of the steering wheel for the purpose of covering the airbag module from the passenger cell.
In the case of a steering wheel having an airbag module, which is covered from the passenger cell by a cap running separately from the steering wheel on the upper side thereof, according to the invention, the airbag module and the cap are fixed separately from each other on the steering wheel in the area of the airbag module. The airbag module is connected to the steering wheel by at least one of a vibration damping or elastic element.
With this arrangement, according to the invention, the airbag module is vibrationally disengaged from the steering wheel when using a vibration damping element while the cap is connected to the steering wheel, without vibrational disconnection. In the event of vibration of the steering wheel, the cap running separately from the steering wheel on the upper side thereof oscillates together with the steering wheel, so that no relative movement takes place between the two. It is thereby possible to keep the gap between the steering wheel and cap small. Fitting an additional mass on the steering wheel to shift the inherent frequency is not necessary.
When using at least one vibration damping element through a phase displacement of the vibration of the airbag module, the inherent frequency of the overall system is shifted into areas in the motor vehicle that are not critical. This is reached, in particular, by matching the damping value of the vibration damping element to the mass of the vibrating module.
As subassemblies of the airbag module, a gas generator, a gas bag retaining plate, a gas bag and a folding chamber restriction plate with cover, are fixed on at least one support plate that is connected to the steering wheel by the vibration damping or elastic element.
It is expedient to provide a connecting plate between the steering wheel and the vibration damping or elastic element.
Each vibration damping element is preferably formed like a bushing and is mounted on a screw with a nut, wherein between the vibrating damping element and the screw head or nut a generator support plate is fixed as a connecting plate that is connected to the steering wheel skeleton and on which the cap is fixed.
In a further embodiment, each connecting plate is bent to a round hook shape at its upper end. The cap has an edge projecting into the steering wheel. The cap edge has apertures in which the upper ends of the connecting plates are locked.
Each connecting plate can be connected directly to the steering wheel skeleton. In a further development it is proposed that each connecting plate is fixed on a contact bridge that in turn is connected to the steering wheel skeleton. In this embodiment the cap is then likewise connected by the connecting plates to the contact bridge so that by pressing down the cap in a known way contacts are brought into connection with each other to operate the horn.
When using elastic elements, there are preferably three elastic elements arranged at the same angular spacing that extend between at least one support plate as a generator support and at least one connecting plate as a generator retaining plate.
In a further embodiment, a ring-shaped elastic element is mounted between the steering wheel hub formed as the generator support, and the airbag module.
The property of the elastic element is thus matched to the mass of the vibrating airbag module so that through a phase displacement of the vibration of the airbag module the inherent frequency of the overall system is moved into non-critical areas. The elastic elements are preferably made of elastomer.